Over three million pregnant women labor and give birth in the United States every year. Despite the frequency of this event, many aspects of labor management lack evidence. The second stage of labor, defined as the interval from complete cervical dilation through delivery of the fetus, is the most physiologically demanding period of labor for both the mother and the fetus. Despite the huge impact labor management can have on mode of delivery and neonatal and maternal morbidities, the optimal technique for managing maternal pushing during the second stage of labor is unknown. The two most common approaches involve either allowing for spontaneous descent (delayed pushing) or initiating pushing with uterine contractions once complete cervical dilation occurs (immediate pushing). Prior studies comparing these approaches reported results that are contradictory with regard to benefit and harm to the neonate and mother. Despite these data, delayed pushing gained wide spread use with a perception that it improves rates of vaginal delivery and reduces morbidities. By contrast, our recent meta-analysis demonstrated that among high-quality trials, delayed pushing did not improve the spontaneous vaginal delivery rate, but prolonged second stage duration. Notably, the largest trial evaluated outcome measures that are obsolete in contemporary obstetrics in the United States, such as use of mid-pelvic rotational forceps. Results of our large observational study indicated that selection to delayed pushing is associated with worse labor outcomes than immediate pushing. The lack of a modern, large, well- controlled, randomized clinical trial to address this question has led to uncertainty as to which technique for maternal pushing in the second stage of labor optimizes outcomes. In addition, effects of immediate versus delayed pushing on risk of maternal pelvic floor injury remain unknown. Given that approximately 11,000 women labor and deliver daily in the United States, there is an urgent need to fill this important clinical knowledge gap and provide high-quality evidence to inform contemporary obstetric management of the second stage of labor. We propose a large, multicenter, randomized clinical trial of immediate versus delayed pushing for nulliparous women in labor at term reaching complete cervical dilation. Our central hypothesis is that immediate pushing in the second stage of labor increases spontaneous vaginal delivery, shortens duration of the second stage, and reduces adverse neonatal and maternal outcomes in nulliparous women. We will pursue the following specific aims: 1) Assess the effectiveness of immediate pushing at complete cervical dilation on the rate of spontaneous vaginal delivery in nulliparous women (Primary Aim), 2) Determine the effect of immediate pushing on the rate of neonatal composite morbidity (Secondary Aim #1), and 3) Determine the impact of immediate versus delayed pushing on objective and subjective measures of maternal pelvic floor morbidity (Secondary Aim #2). We estimate that randomizing a total of 3184 women will provide adequate statistical power to detect meaningful differences in the primary and secondary outcomes.